Recently, an ultrasound system has been extensively used in the medical field due to its non-invasive and non-destructive nature. Modern high-performance ultrasound imaging diagnostic systems and techniques are commonly used to produce two- or three-dimensional ultrasound images of internal features of patients. In order to provide the ultrasound images, the ultrasound system operates in various image modes such as a brightness mode, a Doppler mode and the like to acquire ultrasound images for diagnosis.
In the Doppler mode, the ultrasound system provides a color flow image visualizing velocities of moving objects such as blood flow, heart, etc. The color flow image may be formed based on Doppler signals obtained by alternately transmitting and receiving ultrasound signals to and from a target object at a pulse repetition frequency (PRF). The Doppler signals may include low frequency signals (the so-called clutter signals) due to the motion of a cardiac wall or valve of a heart. The clutter signals may have amplitudes, which are over 100 times than those of pure Doppler signals indicative of velocities of the blood flow. The clutter signals may be an obstacle to accurately detecting velocities of the blood flow. Thus, it is required to remove the clutter signals from the Doppler signals for accurate velocity detection of the blood flow. Since the eigenvector-based clutter filtering is carried out by reflecting characteristics of the Doppler signals, the performance of the eigenvector-based clutter filtering may exceed that of the infinite impulse response filtering. Thus, it has been required to appropriately set eigenvectors for the improved eigenvector-based clutter filtering.